As a system for charging a battery of an electric vehicle or a plug-in hybrid car, there has been developing a method that transfers power to the vehicle in contactless manner by using electromagnetic induction, as illustrated in FIG. 17. Such a method transfers power from a primary transformer (power transmission coil) 10 installed on the ground to a secondary transformer (power reception coil) 20 of the contactless power transfer transformer, installed on a floor of the vehicle.
In the following Patent Literature 1, as the power transmission coil and the power reception coil of the contactless power transfer transformer used in this system, there is disclosed a configuration in which an electric wiring is wound in a flattened circle and provided on one face of a flat plate ferrite magnetic core 21, 31, as illustrated in FIGS. 18A and 18B. Such a coil is referred to as “one-side wound coil” since the winding wires 22, 23 are wound only at one side of the ferrite magnetic cores 21, 31. FIG. 18A is a cross sectional view of the power transmission coil and the power reception coil, and FIG. 18B is a plan view of the power transmission coil and the power reception coil.
The power transfer efficiency of the contactless power transfer transformer that uses the one-side wound coil largely decreases when a vehicle is stopped at a position different from a vehicle stop position and the power transmission coil and the power reception coil do not oppose each other, or when a gap between the power transmission coil and the power reception coil changes. In order to increase the permissible amount with respect to the positional variation or the gap variation, it becomes necessary to increase the sizes of the power transmission coil and the power reception coil.
In the following Patent Literature 2, there is disclosed a contactless power transfer transformer with large permissible amount for the positional variation and the gap variation and that can be configured small in size. As illustrated in FIGS. 20A and 20B 19A and 19B, in such a contactless power transfer transformer, the power transmission coil and the power reception coil are configured by winding the winding wires 62, 64 around the ferrite cores 61, 63. Such a coil is referred to as “both-sides wound coil”. Further, as illustrated in FIG. 19B, the “square core” is used as the ferrite cores 61, 63. FIG. 19A is a cross sectional view of the power transmission coil and the power reception coil, and FIG. 19B is a plan view of the power transmission coil and the power reception coil.
In the contactless power transfer transformer, a main magnetic flux 67 that circles around the magnetic pole portions of the ferrite cores 61, 63 is generated.
Additionally, bypassing leakage magnetic fluxes 68, 69 are generated on the non-opposing sides of the power transmission coil and the power reception coil. If the leakage magnetic fluxes 68, 69 enter an iron plate or the like of the floor of the vehicle, induced current flows through the iron plate and the iron plate is heated, thereby the power transfer efficiency decreases. In order to avoid the decrease in the power transfer efficiency, it is required to magnetically shield the leakage magnetic fluxes 68, 69 by arranging non-magnetic good conductors 65, 66 such as an aluminum plate at back faces of the power transmission coil and the power reception coil.
Further, in the following Patent Literature 3, in order to further decrease a size and weight of the both-sides wound coil, there is disclosed a power transmission coil and a power reception coil as illustrated in FIGS. 20A to 20F. According to such a power transmission coil and a power reception coil, a ferrite core is configured in H-shape, parts 41 and 42 arranged at both ends of the H-shape and being parallel to each other are provided as magnetic pole portions, and a winding wire 50 is wound around a part 43 (the part connects between the magnetic pole portions, and is also referred to as a wound portion) corresponding to a horizontal pole of the H-shape. FIG. 20A is a state in which the winding wire 50 is wound around the ferrite core 40, and FIG. 20D is a state in which the winding wire 50 is not wound around the ferrite core 40. Further, FIG. 20B is a cross sectional view taken along a line A-A of FIG. 20A, and FIG. 20C is a cross sectional view taken along a line B-B of FIG. 20A. Similarly, FIG. 20E is a cross sectional view taken along a line A-A of FIG. 20D, and FIG. 20F is a cross sectional view taken along a line B-B of FIG. 20D.
Here, a case is considered in which the power transmission coil and the power reception coil each configured by a both-sides wound coil by using this H-shape core are arranged to oppose each other with a spacing therebetween at a normal gap length of 70 mm and the power transfer of 3 kW is performed. In such a case, the following power transfer properties are obtained. In particular, the efficiency of the transformer is 95%, the permissible amount of positional variation in the left and right direction (y-direction in FIG. 20A) is ±150 mm, the permissible amount of positional variation in the front and back direction (x-direction in FIG. 20A) is ±60 mm, and the efficiency at which the normal gap length is increased to 100 mm is 92%.